<html>
<body>
<form action="calc.php" method="post">
<input type="text"  name="t2"/>
<select name="op">
    <option value="+">+</option>
    <option value="-">-</option>
    <option value="*">*</option>
    <option value="/">/</option>
</select>
<input type="text" name="t1"/>=
<input type="text"  name="t3">
<input type="submit" value="计算" name="btn" >
</form>
</body>
</html>

<?php

function _get($str){
    $val = !empty($_GET[$str]) ? $_GET[$str] : null;
    return $val;
}

$num1=_get("num1");

$num2=_get("num2");

echo $num1;

?>